The present invention relates generally to antennas, and more particularly, to scanning cup-dipole antenna(s) having a fixed dipole(s) and a rotating cup.
Conventional cup-dipole antennas have been used extensively to provide high aperture efficiency for small antenna apertures that span approximately one wavelength. The cup is formed from a cylindrical conductor shorted at its base with a conducting plate. A dipole is recessed within the cup and has a coaxial transmission line penetrating the base of the cup. A conventional method for achieving a scanned beam is to rotate the dipole and cup assembly as a single unit, necessitating the use of an RF joint such as a flexible coaxial cable or a rotary joint. However, conventional RF joints, particularly rotary joints, are very expensive to design and manufacture. RF joints present a reliability concern for long-life spacecraft, and are susceptible to passive intermodulation (PIM) generation and multipaction for space applications. RF joints are generally massive and clumsy to package, and produce undesirable Ohmic loss and reflections. Thus, conventional antennas do not employ rotation of the cup while the dipole/feed assembly remains fixed. As a consequence, an RF joint has been required with its inherent disadvantages mentioned above.
A better understanding of Conventional cup-dipole antennas may be had from a reading of a book entitled "Microwave Cavity Antennas", by A. Kunar and H. D. History, published by Artech House, Boston (1989). Specific reference is made to Chapter 5 which discusses various conventional cup-dipole antennas.
Accordingly, it is an objective of the present invention to provide for improved scanning cup-dipole antenna(s) having a fixed dipole(s) and a rotating cup.